Trailing arm suspension systems are known and are today commonly used on various vehicles including, for example, heavy duty trucks, semi-trucks, trailers, etc. Typically, a driven or a non-driven axle is secured to the vehicle frame with a pair of trailing arms. The trailing arms extend longitudinally under the vehicle frame and, at one end thereof, are rigidly or otherwise secured to the axle. At their other ends, the trailing arms are pivotally secured to hanger brackets which are, in turn, secured to the vehicle frame. Air and/or coil springs are provided between the vehicle frame and the trailing arms or the axle whereby the vehicle weight is transferred therethrough and to the axle and wheels. Shock absorbers are also typically provided between the vehicle frame and the trailing arms and/or the axle.
For increasing the load capacity of the suspension system, typically, the wall of the axle must be thickened to resist bending. Additionally, because most failures occur at the interconnection between the trailing arm and the axle, various trailing arm to axle connecting structures and methods have been devised. Moreover, to decrease the weight of the axle variable wall thickness axles have been devised. Examples of such prior art suspension systems and axles are shown in: Urschel et al, U.S. Pat. No. 2,256,065; Blessing et al, U.S. Pat. No. 7,090,309; Friedman, U.S. Pat. No. 2,165,472; Wilber, U.S. Pat. No. 2,368,695; Scheel; U.S. Pat. No. 3,037,818; Benteler et al, U.S. Pat. No. 3,668,918; Simon, U.S. Pat. No. 4,435,972; Wilch et al, U.S. Pat. No. 6,230,540; Dilling et al, U.S. Pat. No. 5,366,237; Morris et al, U.S. Pat. No. 6,240,806; Dozier, U.S. Pat. No. 4,452,347; Baroni, U.S. Pat. No. 4,854,427; Smith et al, U.S. Pat. No. 6,241,266; Masser, U.S. Pat. No. 3,482,854; Pierce, U.S. Pat. No. 4,615,539; and, Galazin et al, U.S. Pat. No. 5,112,078.
Notwithstanding all the prior known trailer arm suspension systems, a need still exists for a rugged, heavy duty suspension system which is relatively light weight and is relatively inexpensive to manufacture.